Amyloid-Negative, Neurodegeneration-Negative Amnestic Mild Cognitive Impairment

Background: The concept of amnestic mild cognitive impairment (aMCI) was developed to identify patients at an initial stage of Alzheimer's disease (AD). However, some patients with aMCI do not present biomarkers of amyloid pathology or neuronal injury. Objective: To know the natural history of amyloid-negative and neurodegeneration-negative patients with aMCI, namely to ascertain: 1) whether these patients remain cognitively stable or they present a slow decline in neuropsychological tests; 2) whether the memory complaints subside with the apparently benign clinical course of the disorder or if they persist along the time. Methods: Patients who fulfilled criteria for aMCI with no biomarkers of amyloid pathology or neuronal injury were selected from a large cohort of non-demented patients with cognitive complaints, and were followed with clinical and neuropsychological assessments. Results: Twenty-one amyloid-negative and neurodegeneration-negative aMCI patients were followed for 7.1 +/- 3.7 years. At the baseline they had more pronounced deficits in verbal learning (California Verbal Learning Test) and were also impaired in Word Recall and Logical Memory. However, they did not decline in any cognitive test during follow-up. The patients maintained a high level of subjective memory complaints from baseline (9.7 +/- 4.1) to the follow-up visit (9.2 +/- 4.1, a nonsignificant difference), in spite of a statistically significant decrease in the depressive symptoms, with Geriatric Depression Scale (15 items) score 4.9 +/- 2.8 at baseline and 3.2 +/- 1.8 at the follow-up visit. Conclusions: Amyloid-negative, neurodegeneration-negative aMCI is a chronic clinical condition characterized by the longterm persistence of cognitive deficits and distressing memory complaints. Adequate strategies to treat this condition are needed.